Flag for requestPaint (facebook#31805)

Will run a quick experiment for this.

Author: rickhanlonii

packages/scheduler/src/SchedulerFeatureFlags.js

@@ -14,3 +14,4 @@ export const frameYieldMs = 5;
 export const userBlockingPriorityTimeout = 250;
 export const normalPriorityTimeout = 5000;
 export const lowPriorityTimeout = 10000;
+export const enableRequestPaint = true;

packages/scheduler/src/__tests__/Scheduler-test.js

@@ -18,6 +18,7 @@ let scheduleCallback;
 let requestPaint;
 let shouldYield;
 let NormalPriority;
+let SchedulerFeatureFlags;
 
 // The Scheduler implementation uses browser APIs like `MessageChannel` and
 // `setTimeout` to schedule work on the main thread. Most of our tests treat
@@ -42,6 +43,7 @@ describe('SchedulerBrowser', () => {
     NormalPriority = Scheduler.unstable_NormalPriority;
     requestPaint = Scheduler.unstable_requestPaint;
     shouldYield = Scheduler.unstable_shouldYield;
+    SchedulerFeatureFlags = require('../SchedulerFeatureFlags');
   });
 
   afterEach(() => {
@@ -199,7 +201,9 @@ describe('SchedulerBrowser', () => {
     runtime.assertLog([
       'Message Event',
       'Task',
-      'Yield at 0ms',
+      SchedulerFeatureFlags.enableRequestPaint
+        ? 'Yield at 0ms'
+        : `Yield at ${SchedulerFeatureFlags.frameYieldMs}ms`,
       'Post Message',
     ]);
 

packages/scheduler/src/forks/Scheduler.js

@@ -18,6 +18,7 @@ import {
   userBlockingPriorityTimeout,
   lowPriorityTimeout,
   normalPriorityTimeout,
+  enableRequestPaint,
 } from '../SchedulerFeatureFlags';
 
 import {push, pop, peek} from '../SchedulerMinHeap';
@@ -458,7 +459,7 @@ let frameInterval = frameYieldMs;
 let startTime = -1;
 
 function shouldYieldToHost(): boolean {
-  if (needsPaint) {
+  if (enableRequestPaint && needsPaint) {
     // Yield now.
     return true;
   }
@@ -473,7 +474,9 @@ function shouldYieldToHost(): boolean {
 }
 
 function requestPaint() {
-  needsPaint = true;
+  if (enableRequestPaint) {
+    needsPaint = true;
+  }
 }
 
 function forceFrameRate(fps: number) {
@@ -494,7 +497,9 @@ function forceFrameRate(fps: number) {
 }
 
 const performWorkUntilDeadline = () => {
-  needsPaint = false;
+  if (enableRequestPaint) {
+    needsPaint = false;
+  }
   if (isMessageLoopRunning) {
     const currentTime = getCurrentTime();
     // Keep track of the start time so we can measure how long the main thread

packages/scheduler/src/forks/SchedulerFeatureFlags.www-dynamic.js

@@ -14,3 +14,4 @@
 export const userBlockingPriorityTimeout = 250;
 export const normalPriorityTimeout = 5000;
 export const lowPriorityTimeout = 10000;
+export const enableRequestPaint = __VARIANT__;

packages/scheduler/src/forks/SchedulerFeatureFlags.www.js

@@ -14,6 +14,7 @@ export const {
   userBlockingPriorityTimeout,
   normalPriorityTimeout,
   lowPriorityTimeout,
+  enableRequestPaint,
 } = dynamicFeatureFlags;
 
 export const frameYieldMs = 10;